Problem: $\dfrac{12}{10} + \dfrac{13}{100} = {?}$
The fractions must have the same denominator before you can add them. Rewrite $\dfrac{12}{10}$ as $\dfrac{120}{100}$ $\dfrac{120}{100} + \dfrac{13}{100} = {?}$ $ = \dfrac{133}{100}$